In-situ battery health detector and end-of-life indicator

ABSTRACT

Some embodiments provide a system that monitors a battery in a portable electronic device. During operation, the system applies a pulse load to the battery and determines an impedance of the battery by measuring a voltage of the battery during the pulse load. Next, the system assesses a health of the battery based on the impedance. Finally, the system uses the assessed health to manage use of the battery in the portable electronic device.

BACKGROUND

1. Field

The present embodiments relate to batteries for portable electronicdevices. More specifically, the present embodiments relate to in-situbattery health detectors and end-of-life-indicators within portableelectronic devices.

2. Related Art

Portable electronic devices, such as laptop computers, portable mediaplayers, and/or mobile phones, typically operate using a battery.Furthermore, high-energy battery designs for portable devices ofteninclude battery packs that contain battery cells connected together invarious series and parallel configurations. For example, a six-cellbattery pack of lithium cells may be configured in a three in series,two in parallel (3s2p) configuration. If a single cell can provide amaximum of 3 amps with a voltage ranging from 2.7 volts to 4.2 volts,then the battery pack may have a voltage range of 8.1 volts to 12.6volts and provide 6 amps of current. The charge in such batteries may bemanaged by a circuit board, which is commonly known as a protectioncircuit module (PCM) and/or battery management unit (BMU).

However, once a battery is created, the battery's capacity may diminishover time from use, age, lack of maintenance, damage, and/ormanufacturing defects. For example, oxidation of electrolyte and/ordegradation of cathode and anode material within a battery may be causedby repeated charge cycles and/or age, which in turn may cause a gradualreduction in the battery's capacity. As the battery continues to age anddegrade, the capacity's rate of reduction may increase. Once the batteryreaches 80% of initial capacity, the battery's useful life may beexpended.

Subsequent use of a battery beyond the battery's end-of-life may causeswelling of the battery's cells and may potentially damage the devicepowered by the battery, while providing little charge to the device.However, conventional battery-monitoring mechanisms may only provide arough estimate of the battery's state-of-charge and may not includefunctionality to assess the battery's health. As a result, a user of thebattery may not be aware of the battery's age and/or degradation and maycontinue using the battery beyond the battery's end-of-life.

Hence, what is needed is a mechanism for assessing battery health andend-of-life and managing battery use based on the assessed health.

SUMMARY

Some embodiments provide a system that monitors a battery in a portableelectronic device. During operation, the system applies a pulse load tothe battery and determines an impedance of the battery by measuring avoltage of the battery during the pulse load. Next, the system assessesa health of the battery based on the impedance. Finally, the system usesthe assessed health to manage use of the battery in the portableelectronic device.

In some embodiments, determining the impedance of the battery involves:

-   -   (i) measuring the voltage of the battery in a fully charged        state;    -   (ii) calculating a drop in the voltage after the pulse load is        applied; and    -   (iii) dividing the drop in the voltage by a current of the pulse        load.

In some embodiments, assessing the health of the battery based on theimpedance involves monitoring a change in the impedance over time todetect degradation in the battery.

In some embodiments, monitoring the change in impedance over timeinvolves analyzing a linearity of the impedance as a function of anumber of charge-discharge cycles performed on the battery.

In some embodiments, a lack of linearity corresponds to degradation inthe battery.

In some embodiments, using the assessed health to manage use of thebattery in the portable electronic device involves at least one ofadjusting a charge voltage for the battery, notifying a user of theportable electronic device of an end-of-life for the battery, andisolating a cell in the battery.

In some embodiments, adjusting the charge voltage for the batteryinvolves decreasing the charge voltage to extend a cycle life of thebattery and to control cell swelling within the battery.

In some embodiments, adjusting the charge voltage for the batteryinvolves stopping charging of the battery at the end-of-life for thebattery.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic of a system in accordance with an embodiment.

FIG. 2A shows an exemplary plot of battery voltages in accordance withan embodiment.

FIG. 2B shows an exemplary plot of impedance for a battery in accordancewith an embodiment.

FIG. 3 shows a flowchart illustrating the process of monitoring abattery in a portable electronic device in accordance with anembodiment.

FIG. 4 shows a flowchart illustrating the process of determining theimpedance of a battery in accordance with an embodiment.

FIG. 5 shows a computer system in accordance with an embodiment.

In the figures, like reference numerals refer to the same figureelements.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the embodiments, and is provided in the contextof a particular application and its requirements. Various modificationsto the disclosed embodiments will be readily apparent to those skilledin the art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present disclosure. Thus, the present invention is notlimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. The computer-readable storage medium includes, but is notlimited to, volatile memory, non-volatile memory, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs),DVDs (digital versatile discs or digital video discs), or other mediacapable of storing code and/or data now known or later developed.

The methods and processes described in the detailed description sectioncan be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above. When a computersystem reads and executes the code and/or data stored on thecomputer-readable storage medium, the computer system performs themethods and processes embodied as data structures and code and storedwithin the computer-readable storage medium.

Furthermore, methods and processes described herein can be included inhardware modules or apparatus. These modules or apparatus may include,but are not limited to, an application-specific integrated circuit(ASIC) chip, a field-programmable gate array (FPGA), a dedicated orshared processor that executes a particular software module or a pieceof code at a particular time, and/or other programmable-logic devicesnow known or later developed. When the hardware modules or apparatus areactivated, they perform the methods and processes included within them.

Embodiments provide a method and system for monitoring a battery in aportable electronic device. The battery may include one or more cells ina parallel and/or series configuration and supply power to a mobilephone, laptop computer, portable media player, and/or peripheral device.In addition, the battery may be reused up to a number of charge cyclesbefore losing enough capacity to reach an end-of-life.

More specifically, embodiments provide an in-situ method and system forassessing the health of the battery and determining the end-of-life forthe battery. The battery's health may be assessed by monitoring thebattery's impedance as charge cycles are performed on the battery. Theimpedance may be calculated by measuring the battery's voltage duringapplication of a pulse load to the battery, calculating the drop involtage after the pulse load is applied, and dividing the drop involtage by the current of the pulse load. As a new battery is used andrecharged, the impedance may increase linearly as a function of thenumber of charge-discharge cycles performed on the battery. However, alack of linearity in the change in impedance may indicate degradation,damage, defects, and/or the end-of-life for the battery. For example, aninitial lack of linearity (e.g., an inflection point) in the change inimpedance may represent the onset of degradation in the battery, whilesubsequent nonlinear increases in the impedance may represent thebattery's end-of-life.

The assessed health of the battery may then be used to manage use of thebattery in the portable electronic device. For example, the assessedhealth may be used to adjust a charge voltage for the battery (e.g., toextend the battery's cycle life at the onset of degradation, controlcell swelling within the battery, and/or terminate use of the battery atthe end-of-life), notify a user of the portable electronic device of thebattery's end-of-life, and/or isolate a cell in the battery (e.g., fromdamage or defects). Consequently, embodiments may both extend the usefullife of the battery and prevent continued use of the battery beyond theend-of-life.

FIG. 1 shows a schematic of a system in accordance with an embodiment.The system may provide a power source to a portable electronic device,such as a mobile phone, personal digital assistant (PDA), laptopcomputer, portable media player, and/or peripheral device. In otherwords, the system may correspond to a battery that supplies power to aload 118 from one or more components (e.g., processors, peripheraldevices, backlights, etc.) within the portable electronic device. Asshown in FIG. 1, the system includes a number of cells 102-106, a set ofswitches 110-114, a main power bus 116, a system microcontroller (SMC)120, and a set of monitors 124-128.

In one or more embodiments, cells 102-106 are connected in a parallelconfiguration with one another using main power bus 116. Each cell102-106 may include a sense resistor (not shown) that measures thecell's current. Furthermore, the voltage and temperature of each cell102-106 may be measured with a thermistor (not shown), which may furtherallow a battery “gas gauge” mechanism to determine the cell'sstate-of-charge, impedance, capacity, charging voltage, and/or remainingcharge. Measurements of voltage, current, temperature, and/or otherparameters associated with each cell 102-106 may be collected by acorresponding monitor 124-128. Alternatively, one monitoring apparatusmay be used to collect sensor data from multiple cells 102-106 in thebattery.

Data collected by monitors 124-128 may then be used by SMC 120 to assessthe state of charge, capacity, and/or health of cells 102-106. SMC 120may also use the data to manage use of the battery in the portableelectronic device. For example, SMC 120 may correspond to a managementapparatus that uses the state of charge of each cell 102-106 to adjustthe charging and/or discharging of the cell by connecting ordisconnecting the cell to main power bus 116 using a set of switches110-114. Fully discharged cells may be disconnected from main power bus116 during discharging of the battery to enable cells with additionalcharge to continue to supply power to load 118. Along the same lines,fully charged cells may be disconnected from main power bus 116 duringcharging of the battery to allow other cells to continue charging.

Those skilled in the art will appreciate that reductions in batterycapacity may result from factors such as age, use, defects, and/ordamage. Furthermore, a decrease in battery capacity beyond a certainthreshold (e.g., below 80% of initial capacity) may result in swellingof the battery, which may damage the portable electronic device, whileproviding little useful charge to the portable electronic device. Inother words, the battery may reach an end-of-life once the battery'scapacity drops below the threshold and may require replacement and/ordiscontinuation of use.

In one or more embodiments, the system of FIG. 1 corresponds to anin-situ system for determining the battery's end-of-life throughperiodic assessment of the battery's health. For example, the system ofFIG. 1 may be implemented by one or more components of the portableelectronic device connected to the battery. To assess the battery'shealth, monitors 124-128 may measure the voltage of cells 102-106 in afully charged state and continue measuring while a pulse load is appliedto the battery (e.g., from one or more components, charger 122, and/or adedicated load-generating apparatus or circuit). In one or moreembodiments, the length of the pulse load is inversely proportional tothe magnitude of the pulse load. For example, a pulse load of 10 ampsmay be applied to the battery for 0.5 seconds, while a pulse load of 0.5amps may be applied to the battery for 10 seconds.

Monitors 124-128 may additionally determine the impedance of cells102-106 using the measured voltage. In particular, the impedance of acell may be obtained by calculating the drop in voltage for the cellafter the pulse load is applied and dividing the drop in voltage by thecurrent of the pulse load. For example, a drop in voltage of 0.2 voltsfrom a pulse load of 4 amps may correspond to an impedance of 0.05 ohms.Voltage measurements and impedance calculations are discussed in furtherdetail below with respect to FIG. 2A.

Moreover, SMC 120 may monitor the change in impedance over time todetect degradation in cells 102-106 and/or the battery in general. Asthe battery is used or ages, the impedance may increase linearly untilthe battery reaches a certain number of charge-discharge cycles, afterwhich the impedance may encounter an inflection point and increaselinearly at a higher rate. For example, the impedance may increase at arate of roughly 25 μohms per charge-discharge cycle for the first 200charge cycles, then at a much higher rate of 200 μohms percharge-discharge cycle for the next 100 charge-discharge cycles. As aresult, an inflection point in the change in impedance may be found ataround the 200^(th) charge-discharge cycle.

The change in impedance may also increase nonlinearly as the batteryreaches the end-of-life. For example, the battery's impedance mayincrease sharply at around the 300^(th) charge-discharge cycle andfluctuate nonlinearly beyond the 300^(th) charge-discharge cycle. As aresult, SMC 120 may detect degradation in the battery by analyzing thelinearity of the impedance as a function of the number ofcharge-discharge cycles performed on the battery. An initial lack oflinearity may indicate degradation in the battery, while subsequentnonlinear changes to the impedance may represent the battery'send-of-life. Impedance analysis and linearity is discussed in furtherdetail below with respect to FIG. 2B.

SMC 120 may further use the assessed health of the battery to manage useof the battery in the portable electronic device. If degradation in thebattery is found, SMC 120 may reduce the battery's charge voltage todecrease the rate of cell oxidation in the battery and extend thebattery's cycle life, as well as to control cell swelling within thebattery. If the battery's end-of-life is reached, SMC 120 may notify theuser to prevent continued use of the battery and damage to the portableelectronic device. For example, SMC 120 may illuminate a light-emittingdiode (LED) on the portable electronic device to notify the user of theend-of-life, or SMC 120 may provide the notification through a userinterface and/or display screen of the portable electronic device. SMC120 may also stop charging the battery if all cells 102-106 haveimpedances that indicate end-of-life. On the other hand, SMC 120 mayisolate individual cells 102-106 in the battery if the cells aredefective or damaged and/or have reached the threshold for end-of-lifeearlier than other cells in the battery. For example, SMC 120 maydisconnect cell 102 from main power bus 116 using switches 114 toprevent continued use of cell 102 in the battery if cell 102 has reached80% of initial capacity before cells 104-106.

Those skilled in the art will appreciate that the functionality of SMC120 and/or monitors 124-128 may be implemented in multiple ways. Forexample, SMC 120 and monitors 124-128 may be implemented using one ormore hardware modules (e.g., integrated circuits) in the portableelectronic device. Similarly, a portion of the functionality of SMC 120and/or monitors 124-128 may be implemented in software that executes ona processor of the portable electronic device. In other words, themonitoring and management of cells 102-106 in the battery may beconducted by different combinations of in-situ hardware and/or softwarecomponents on the portable electronic device.

FIG. 2A shows an exemplary plot of battery voltages 206-208 inaccordance with an embodiment. Voltages 206-208 are shown asmeasurements of volts 202 over time in seconds 204. In addition, eachvoltage measurement includes a voltage drop 210-212 that is caused bythe application of a pulse load 216 to the battery, the current 214 ofwhich is also shown in the plot as a function of time 204.

Voltage 206 may correspond to the voltage measured from the batteryduring the first charge-discharge cycle of the battery. In other words,voltage 206 may be obtained from a new, un-degraded cell and/or battery.As a result, voltage drop 210 of voltage 206 may be smaller than voltagedrops of subsequent voltage measurements (e.g., voltage 208) obtainedfrom the cell and/or battery. In particular, voltage drop 210 may besmaller than voltage drop 212 of voltage 208, which may be measured fromthe battery during the 300^(th) charge-discharge cycle. As shown in FIG.2A, voltage drop 210 is approximately 0.15 volts, while voltage drop 212is approximately 0.25 volts, indicating an increase of about 0.1 voltsin the voltage drop experienced by the battery during application ofpulse load 216 between the first and 300^(th) charge-discharge cycle.

As mentioned previously, voltage drops 210-212 may be used to calculateimpedances for the battery, which in turn may be used to assess thehealth of the battery. To determine the impedances, voltage drops210-212 may be divided by the amount of current 214 applied during pulseload 216. Using a value of 4.5 amps for current 214 of pulse load 216may produce an impedance of approximately 0.03 ohms during the firstcharge-discharge cycle of the battery and an impedance of approximately0.056 ohms during the 300^(th) charge-discharge cycle. As discussedbelow with respect to FIG. 2B, changes in the impedance over time may beused to assess the health of the battery and detect the end-of-life forthe battery.

FIG. 2B shows an exemplary plot of impedance 218 for a battery inaccordance with an embodiment. Impedance 218 is plotted in μohms 220 asa function of a number of charge-discharge cycles 222 performed on thebattery. As described above, impedance 218 may be obtained by measuringthe battery's drop in voltage as a pulse load is applied and dividingthe drop in voltage by the current of the pulse load.

In one or more embodiments, impedance 218 corresponds to an indicator ofhealth and/or age for the battery. As shown in FIG. 2B, the change inimpedance 218 is roughly linear for the first 200 charge-dischargecycles, increasing at a rate of about 25 μohms per charge-dischargecycle. During this period, the battery's capacity may diminish steadily,but the battery may still be in a good state of health. However, afterabout 200 cycles, the change in impedance increases significantly toabout 200 μohms per charge-discharge cycle and progresses linearly foranother 100 cycles. The increased change in impedance may representdegradation in the battery and a significant loss in capacity. Finally,at about 300 charge-discharge cycles, the change in impedance 218increases even more sharply and becomes nonlinear. Once the change inimpedance 218 is nonlinear, the end-of-life for the battery may bereached. At this point, the battery may provide little useful charge andmay begin to swell if the battery continues to be used.

Consequently, the linearity of impedance 218 as a function of number ofcharge-discharge cycles 222 may be analyzed to assess the health of thebattery and to manage use of the battery. In particular, the chargevoltage of the battery may be decreased during the inflection point ataround 200 charge-discharge cycles to extend the cycle life of thebattery and/or to control cell swelling within the battery. In addition,a notification of end-of-life may be provided and/or charging of thebattery may be stopped when the battery reaches 300 charge-dischargecycles to minimize use of the battery after the end-of-life is reached.

Impedance 218 may also be used to detect damage and/or defects in one ormore cells of the battery. For example, if a nonlinear increase inimpedance 218 is found in a cell prior to 300 charge-discharge cycles,defects and/or damage may be present in the battery. As a result, anotification may be generated and/or the cell may be disconnected fromthe battery. If all cells of the battery display nonlinear increases inimpedance, the battery may be disconnected from the portable electronicdevice to prevent further use of the battery.

FIG. 3 shows a flowchart illustrating the process of monitoring abattery in a portable electronic device in accordance with anembodiment. In one or more embodiments, one or more of the steps may beomitted, repeated, and/or performed in a different order. Accordingly,the specific arrangement of steps shown in FIG. 3 should not beconstrued as limiting the scope of the embodiments.

Initially, a pulse load is applied to the battery (operation 302). Thepulse load may be generated by an integrated circuit connected to thebattery that functions as a load-generating apparatus. For example, thepulse load may be generated by a charger for the battery and may be 0.5to 10 amps in magnitude and 0.5 to 10 seconds in duration. Next, theimpedance of the battery is determined by measuring the voltage of thebattery during the pulse load (operation 304). The health of the batteryis then assessed based on the impedance (operation 306). As discussedabove, the health of the battery may be based on the linearity of theimpedance as a function of the number of charge-discharge cyclesperformed on the battery. Finally, the assessed health is used to managethe use of the battery in the portable electronic device (operation308). For example, the assessed health may be used to adjust a chargevoltage for the battery (e.g., to extend a cycle life of the battery, tocontrol cell swelling within the battery, and/or to stop charging of thebattery), notify a user of the portable electronic device of anend-of-life for the battery, and/or isolate a cell in the battery.

FIG. 4 shows a flowchart illustrating the process of determining theimpedance of a battery in accordance with an embodiment. In one or moreembodiments, one or more of the steps may be omitted, repeated, and/orperformed in a different order. Accordingly, the specific arrangement ofsteps shown in FIG. 4 should not be construed as limiting the scope ofthe embodiments.

First, the voltage of the battery in a fully charged state is measured(operation 402). Next, the drop in voltage after the pulse load isapplied is calculated (operation 404). Because the voltage is alwaysmeasured when the battery is fully charged, changes in the drop involtage may represent cell oxidation, damage, and/or defects in thebattery instead of changes to the battery's state-of-charge. Newerbatteries may experience lower drops in voltage than older, defective,and/or damaged batteries. Finally, the drop in voltage is divided by thecurrent of the pulse load (operation 406) to obtain the impedance.

FIG. 5 shows a computer system 500 in accordance with an embodiment.Computer system 500 includes a processor 502, memory 504, storage 506,and/or other components found in electronic computing devices. Processor502 may support parallel processing and/or multi-threaded operation withother processors in computer system 500. Computer system 500 may alsoinclude input/output (I/O) devices such as a keyboard 508, a mouse 510,and a display 512.

Computer system 500 may include functionality to execute variouscomponents of the present embodiments. In particular, computer system500 may include an operating system (not shown) that coordinates the useof hardware and software resources on computer system 500, as well asone or more applications that perform specialized tasks for the user. Toperform tasks for the user, applications may obtain the use of hardwareresources on computer system 500 from the operating system, as well asinteract with the user through a hardware and/or software frameworkprovided by the operating system.

In one or more embodiments, computer system 500 provides a system formonitoring a battery in a portable electronic device. The system mayinclude a charger that applies a pulse load to the battery. The systemmay also include a monitoring apparatus that determines an impedance ofthe battery by measuring a voltage of the battery during the pulse load.Finally, the system may include a management apparatus that assesses ahealth of the battery based on the impedance and uses the assessedhealth to manage use of the battery in the portable electronic device.The system may be used to monitor battery health for a battery thatsupplies charge to computer system 500, or the system may correspond toan external monitoring mechanism for a battery from other portableelectronic devices.

In addition, one or more components of computer system 400 may beremotely located and connected to the other components over a network.Portions of the present embodiments (e.g., charger, monitoringapparatus, management apparatus, etc.) may also be located on differentnodes of a distributed system that implements the embodiments. Forexample, the present embodiments may be implemented using a cloudcomputing system that monitors and manages batteries in remote portableelectronic devices.

The foregoing descriptions of various embodiments have been presentedonly for purposes of illustration and description. They are not intendedto be exhaustive or to limit the present invention to the formsdisclosed. Accordingly, many modifications and variations will beapparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention.

What is claimed is:
 1. A computer-implemented method for monitoring abattery in a portable electronic device, comprising: applying a pulseload to the battery; determining an impedance of the battery bymeasuring a voltage of the battery during the pulse load; assessing ahealth of the battery based on the impedance by analyzing a linearity ofthe impedance of the battery for at least two separate charge-dischargecycles performed on the battery; and using the assessed health to manageuse of the battery in the portable electronic device.
 2. Thecomputer-implemented method of claim 1, wherein determining theimpedance of the battery involves: measuring the voltage of the batteryin a fully charged state; calculating a drop in the voltage after thepulse load is applied; and dividing the drop in the voltage by a currentof the pulse load.
 3. The computer-implemented method of claim 1,wherein a lack of linearity corresponds to degradation in the battery.4. The computer-implemented method of claim 1, wherein using theassessed health to manage use of the battery in the portable electronicdevice involves at least one of: adjusting a charge voltage for thebattery; notifying a user of the portable electronic device of anend-of-life for the battery; and isolating a cell in the battery.
 5. Thecomputer-implemented method of claim 4, wherein adjusting the chargevoltage for the battery involves: decreasing the charge voltage toextend a cycle life of the battery and to control cell swelling withinthe battery.
 6. The computer-implemented method of claim 4, whereinadjusting the charge voltage for the battery involves: stopping chargingof the battery at the end-of-life for the battery.